Automobile assembly plants and other facilities that require large conveyor systems often make use of power and free conveyors. A power and free conveyor includes a number of trolleys which travel along conveyor tracks and are equipped with carriers on which partially assembled automobile bodies or other articles are transported between successive work stations. The trolleys are normally propelled by a drive chain which travels continuously along a separate track on wheels connected with the chain. The trolley typically has a pivotal arm which includes a trolley dog. The trolley dog is normally engaged by a drive dog that projects from the chain so that the chain conveys the trolley along the conveyor track. In a commonly used conveyor system known as an inverted power and free conveyor, the drive chain is located below the trolley.
A power and free conveyor is advantageous in many applications because the drive chain runs continuously and all of the carriers are conveyed except for those that are selectively detached from the drive chain so that work can be performed on the objects they carry. Thus, some of the carriers can be stopped without the need to stop all of the others.
It is necessary to provide a power and free conveyor with a stop mechanism that is used to selectively disengage the trolleys from the drive chain so that the carrier can be stopped at the desired locations. Also, it is necessary to stop a carrier that is approaching a preceding carrier that is stopped on the track. Devices that perform the latter function and prevent collisions between carriers are known as accumulators. The present invention is concerned instead with a stop mechanism that may be situated at a selected location along the conveyor track and actuated to stop the next coming trolley adjacent to a work station.
Different types of stop mechanism have been proposed, mostly involving the insertion of a blade in the path of the trolley lever to pivot the lever in a direction to detach the trolley dog from the chain dog. Another type of stop is disclosed in U.S. Pat. No. 4,790,247 to Summa. The present invention is an improvement over all of the foregoing types of stop mechanisms.
Although the stops that have been proposed in the past operate in a satisfactory manner, they are not wholly free of problems. Most notably, the ability of prior stop mechanisms to function reliably over an extended operating life is questionable. Each time the stop mechanism is engaged or released, its parts are subjected to considerable wear which can cause a malfunction when the cumulative effective of the wear builds up to the point where the parts no longer cooperate as intended. If the stop mechanism fails, it is necessary to shut the entire conveyor system down long enough to allow the necessary repairs or replacement to be completed. This can create a significant problem because of the combined effect of the lost production and the costs that are involved in repairing or replacing the stop mechanism.